British Swimming Championships 2010
Dates: 29 March-3 April Venue: Ponds Forge, Sheffield
Live on BBC Radio 5 live sports extra, highlights on this website
'I'm breathing so hard my ribs keep popping out,' said Jackson
Leading British swimmer Jo Jackson may have to write off her 2010 season after a winter in which her asthma worsened.
Jackson's condition is now considered severe having suffered flu and respiratory illnesses in recent months.
"I've had asthma before but I've never been through anything like this and it's been scary," said Jackson ahead of next week's Commonwealth trials.
"I have no expectation of myself this year. Realistically I have a long way to go to be near my best."
Governing body British Swimming is taking advice from specialists before deciding on a next course of action in a bid to restore the 23-year-old to full fitness.
I'm breathing so hard while trying to train that my ribs keep popping out
Jackson claimed Olympic bronze at the 2008 Beijing Games in the women's 400m freestyle event, which was won by British team-mate Rebecca Adlington.
She should have spent a 27-week block of winter training fine-tuning herself for the new season, starting with the British Championships in Sheffield on Monday, which serve as her first qualifying event for the English Commonwealth team.
But illness vastly reduced her training time and left a question mark hanging over her season.
"I'm receiving physio treatment twice a day because I'm breathing so hard while trying to train that my ribs keep popping out," she said.
"I'm desperate to train well and get back to my best but it's hard given my health.
"I'm training the best I can and I am aiming for the Commonwealth Games [this October, in India] and will be targeting qualification events later in the year."
has been reported
that Jackson may seek special permission from the National Health Service to receive an oral asthma drug normally considered a last resort.
Jackson, as an international swimmer competing under strict anti-doping regulations, cannot take forms of medication such as steroids which members of the public would be expected to try first, so would need an exemption to use the drug.
But BBC Sport understands the drug is just one of several options being considered by specialists in a bid to restore Jackson's health, two years ahead of the London 2012 Olympics.
In the meantime, Jackson will look to the English national trials in August to secure qualification for the Commonwealth Games.
It would be devastating if it has an effect on her career just when she was getting so good
BBC Sport's Karen Pickering
Former freestyle relay world champion Karen Pickering, now a BBC Sport summariser, competed for Britain while asthmatic.
"I know how debilitating it is and how it can affect training," said Pickering.
"It's very stressful, very frustrating and all those things trigger asthma as well - which doesn't help. The more tense and nervous Jo Jackson gets leading up to major championships, the more it ends up spiralling.
"I used medication as much as possible but there are limitations because some of the better asthma medication is banned. You can't just take what a non-athlete would take.
"Jo will have some knowledgeable people and a lot of support, and I really hope they sort it out because it would be devastating if it has an effect on her career just when she was getting so good."